The present invention relates to a firing mechanism for a revolver and particularly relates to a firing mechanism which minimizes or eliminates misfires due to wear of the firing pin caused by high pressure gas cutting and jams of the cartridge casings in the chambers of the revolver cylinder caused by postfiring rebound of the casings into the chambers.
Conventional firing mechanisms for revolvers normally have a firing pin carried by the revolver frame for movement between a non-firing position retracted rearwardly of the bolster face and a firing position in which the pin is projected by the hammer across the headspace between the bolster face and the base of the cartridge for penetration of the cartridge base. Particularly, at the end of its forward travel, the firing pin strikes and intrudes or penetrates the primer cup to ignite the primer charge and the main powder charge. Upon ignition of the main powder charge within the cartridge casing, the developing high pressure gases cause the cartridge casing to expand radially and simultaneously move axially rearwardly toward the bolster face.
Frequently, the action of the firing pin when striking the primer cup and/or the displacement of the cartridge casing rearwardly with the firing pin causes the metal of the primer cup to work and stretch. This generates holes in the worked and stretched metal primer cup which permit leakage of the high pressure gas about the firing pin. This, in turn, causes a gas-cutting action on the firing pin. That is, the high pressure gas leaked from the primer cup removes sufficient metal from the firing pin to often quickly dull the firing pin and reduce its effectiveness in subsequently firing primers. Particularly, the gas-cutting action erodes and causes a malshaping of the firing pin tip which can and does result in subsequent misfiring of the revolver. The damage to the firing pin is also progressive as the revolver is repeatedly fired resulting in the increasing occurrence of misfires.
Considered from another standpoint, the bullet and the cartridge casing are separated upon ignition. Since the casing weighs less than the bullet, it accelerates rearwardly at a higher velocity than the bullet moves forwardly. When the casing reaches the bolster face of the revolver, the bullet moves forwardly at high velocity for passage through the revolver barrel. The firing pin is conventionally coupled to the hammer. The firing pin and hammer are the only mechanically coupled mechanism for preventing rearward movement of the casing. While the mass of the hammer is heavier than that of the bullet, the surface contact between the firing pin and the primer cup is not large enough to move the hammer backwards in time to retract the firing pin without excessive metal deformation and working of the metal of the primer cup and consequent piercing of the primer cup. A shortening of the firing pin to avoid excessive metal working and deformation can stop the piercing action and consequent gas cutting and erosion of the firing pin. However, if the firing pin is shortened, its protrusion is not great enough to permit striking contact with the primer cup and sufficient penetration of all cartridges of varying lengths, particularly those having relatively short lengths, as discussed below. The problem of misfiring would thus not be cured.
While firing pin erosion occurs to a greater or lesser extent in most of the different types of revolvers, the problem of firing pin erosion in particularly acute in the 9 mm. revolver. In comparison with other cartridges, the 9 mm. cartridge is a higher pressure cartridge which can generate pressures within its casing as high as 40,000 lbs/in.sup.2. This high pressure also indicates appreciably higher gas temperatures inside the cartridge casing than other cartridges. Also, the rate at which pressure is developed in the 9 mm. cartrige is very high. This combination of high pressure and temperature causes the gas escaping through the pierced primer cup at a high rate to very quickly erode the firing pin, even more so than occurs with respect to the firing pins in other types of revolvers.
Cartridges for revolvers also vary in length. Thus, the distance from the bolster face to the base of the cartridge, e.g. the headspace, when the cartridge is fully seated forwardmost in the chamber of the revolver cylinder, varies substantially from cartridge to cartridge as the revolver cylinder is rotated to register the cartridges in firing position. This is particularly true of the 9 mm. cartridge. The gas cutting and erosion of the firing pin is exacerbated the greater the headspace. For example, it will be appreciated that the base of a cartridge of relatively short length, when fully seated forwardmost in its cylinder chamber, will be spaced from the bolster face a greater distance than the spacing between the base of a longer cartridge and the bolster face. Consequently, for cartridges of relatively short lengths, the firing pin has a greater distance, e.g. headspace, to travel to strike the primer cup than the distance traveled by the firing pin when firing cartridges of greater length. More importantly, the cartridge casing of the shorter cartridge has a greater distance to move rearwardly toward the bolster face when the cartridge is fired than does the casing of the relatively longer cartridge when it is fired. When a short cartridge casing moves rearwardly in a revolver having a conventional firing mechanism, it carries the firing pin with it this greater distance causing further stretching and working of the metal of the primer cup than would otherwise be the case for a longer cartridge casing. Consequently, there is a substantially greater tendency to pierce the primer cup and leak high pressure gas about and thereby erode the firing pin in the case of short cartridges. Also, the headspace tends to increase with gun wear further excerbating the problem of piercing the metal of the primer cup and releasing the high pressure gas about the firing pin.
In automatics, an open bolt-type firing pin system is utilized. There, a firing pin is integral with the face of the bolt and is fixed to have a small protrusion ahead of the bolt. The bolt and firing pin are essentially one piece and the bolt reaches out and strikes the rear of the casing. Misfires will not frequently occur and the firing pin protrusion can be kept to a limit which does not permit piercing. However, this system is not applicable to revolvers.
Further, as the high pressure gas resulting from firing the cartridge exerts a radial pressure on the casing and the casing moves rearwardly, the cartridge casing tends to radially enlarge and correspond to the slight rearward taper of the cylinder chamber. On rebound of the hammer and firing pin, the casing is displaced forwardly by and with the firing pin. As a result, there is a tendency of the radially enlarged tapered casing to jam or stick in the chamber on postfire rebound. This problem is exacerbated in shorter cartridges because the greater the rearward distance of travel of the casing, the greater the radial expansion and the greater the tendency for the casing to bind or jam when displaced forwardly on postfire rebound. The elastic recovery of the casing toward its original size is insufficient to permit the casing to fully seat in the chamber in the same position before firing. Soft casings, for example brass, have particularly insufficient elastic recovery. Thus, there is a further tendency for casings formed of soft materials to stick or jam within the chamber upon postfiring rebound.